Pistachio Sugar Cookies

Preheat oven to 175°C. Line a cookie sheet with a cooking paper.
Beat egg whites until the soft peaks form. Add 60 gr. confectioners' sugar and beat until stiff.
Pour the pistachios into the food processor and process until finely chopped, add the remaining sugar, the flour and the lemon zest. Stir well. Add the beaten egg whites very carefully. Drop by teaspoonfuls onto the prepared cookie sheet. Bake about 15 minutes. Cool about 5 minutes on a wire rack. Dust with confectioners' sugar if desired.